Sunday, 20 October 2013

Installation of Hadoop on your Centos 6/RHEL box is now a lot simpler since rpm versions have been made available but you nonetheless need to have installed the JDK prior to doing so.Change the JAVA_HOME path to /usr/java/default and you can install Hadoop via yum from Epel repo.$ sudo yum -y install hadoop

If you have any problems with yum you can also use the Apache mirror service, download your preference and install it with$ sudo rpm -Uvh <rpm_package_name>

Once installed as a package, set it up in two steps.

First set up configuration and start Hadoop processes

$ sudo /usr/sbin/hadoop-setup-single-node.sh

You will be asked a series of questions to which you should answer yes and you should get output similar to below.Welcome to Hadoop single node setup wizard

Would you like to use default single node configuration? (y/n) yWould you like to format name node? (y/n) yWould you like to setup default directory structure? (y/n) yWould you like to start up Hadoop? (y/n) yWould you like to start up Hadoop on reboot? (y/n) y

Baobab is a useful graphical tool for checking the amount of disk space used on your system. It is available in the Epel repo as part of the gnome-utils package which contains a set of small desk accessory utility applications for GNOME, such as a dictionary, a disk usage analyzer, a screenshot tool and others.

Make sure that you have it installed with one of the following commands.$ sudo yum -y install baobab$ sudo yum -y install gnome-utilsNow you can use it with a couple of simple commands.$ baobab /home/anton

Baobab Centos 6

$ baobab

Baobab

Baobab places disk usage analysis in two panels.

Per-directory disk utilization stats are reported in numbers in the left panel whereas the overall disk utilization is visualized in the right panel.

In the ring chart right panel visualisation, multiple concentric circles show the directories from the directory tree, while the center of the circles corresponds to the root of the directory tree.

The smaller a circle is, the higher a corresponding directory ranks in the directory hierarchy. Hovering a mouse over any particular directory will show the names of its sub-directories on the immediate outer circle. The relative sizes of the sub-directories can be assessed by comparing their sizes in a ring-shaped area.

Baobab also uses treemap charts in which overlapping rectangles are implemented to visualize the hierarchical structure of directories, where the outermost rectangle corresponds to the root of the directory tree, and the inner rectangles to sub-directories. The size of each rectangle indicates the size of a corresponding sub-directory. Again, you can hover a mouse to check the name of a sub-directory.

Baobab can analyze local folders as well as remote folders. To examine remote folders, click on “Scan a Remote Folder” button at the far right. Baobap supports SSH, FTP, WebDAV and Windows Share.

Sunday, 13 October 2013

Nagios
is a powerful monitoring system that enables you to identify and
resolve infrastructure problems before they affect critical
processes.

Designed with scalability and
flexibility in mind, Nagios gives you the peace of mind that comes
from knowing your business processes won't be affected
by unknown outages.

Nagios is a powerful tool that
provides you with instant awareness of your organization's
mission-critical IT infrastructure. It allows you to detect and
repair problems and mitigate future issues before they affect
end-users and customers.

Sunday, 6 October 2013

One of the greatest attributes of the Minimal Fluxbox Desktop is the key shortcuts to the most used programs and these are certain to include the likes of Thunar and Rxvt terminal emulator or similar. You can use the F1 through 12 keys amongst others to pop up the programs and I assign F1 and F2 to Thunar and Rxvt respectively. Notwithstanding the fact that the Minimal Desktop can be made headless by simply hitting Ctrl+Alt+F4, there are also a formidable array of commands at your disposal in order to perform tasks from the console or terminal emulator. Below are some of the most used ones.

The following list describes some of the most useful and popular Linux commands. Consult the man page for each command to learn about additional arguments and details of operation.

Searches the manual pages for occurrences of the keyword and prints short descriptions from the beginning of matching manual pages.

# at time

# at -t file time

Executes commands entered via stdin (or, by using the alternative form, the specified file) at the specified time. The time can be specified in a variety of ways; for example, in hour and minute formator in hour, minute, month, day, and year format.

# cal month year

Prints a calender for the specified month of the specified year

Centos 6 calender function

# cat files

Prints out the contents of the specified files

# cd

# cd directory

Changes the current working directory to the user's home directory or the specified directory.

# chgrp group files

# chgrp -R group files

Changes the group of the specified files to the specified group. The alternative form of the command operates recursively, changing the group of subdirectories and files beneath a specified directory. The group must be named in the /etc/groups file, maintained by the newgroup command

# chmod mode files

# chmod -R mode files

Changes the access mode of the specified files to the specified mode. The alternative form of the command operates recursively, changing the mode of subdirectories and files beneath a specified directory.

# chown userid files

# chown -R userid files

Changes the owner of the specified files to the specified userid. The alternative form of the command operates recursively, changing the owner of subdirectories and files beneath a specified directory.

# clear

Clears the terminal screen

# cp file1 file2

# cp files directory

# cp -R files directory

Copies a file to another file or directory, or copies a subdirectory and all its files to another directory.

# date

# date date

Displays the current date and time or changes the system date and time to the specified value.

# df

Prints the amount of free disk space on each mounted filesystem

# diff file1 file2

# Compares the two files, reporting all discrepancies. Similar to the diff command though the output format differs.

# dmesg

Prints the messages resulting from the most recent system boot

# du

# du directories

Prints the amount of disk space used by the current directory (or the specified directories) and subdirectories.

# echo string

# echo -n string

Prints the specified text on the standard output stream. The -n option causes omission of the trailing newline character.

# fdformat device

Formats the media inserted in the specified floppy disk drive. The command performs a low-level format only; it does not create a filesystem. To create a filesystem, issue the mkfs command after formatting the media.

# fdisk device

Edits the partition table of the specified hard disk.

# fg

# fg jobs

Brings the current job (or the specified jobs) to the foreground.

# file files

Determines and prints a description of the type of each specified file.

# find

# find path -name pattern -print

Search for files in a directory hierarchy. Searches the specified path for files with names matching the specified pattern (usually enclosed in single quotes) and prints their names.

# finger users

Prints a description of the specified users (install with yum).

Centos 6 Finger command

# ftp hostname

Opens a FTP connection to the specified host, allowing files to be transfered. The FTP program provides subcommands for accomplishing file transfers.

# grep pattern files

# grep -i pattern files

# grep -n pattern files

# grep -v pattern files

Search the specified files for text matching the specified pattern (usually enclosed in single quotes) and print matching lines. The -i option specifies that matching is performed without regard to case. The -n option specifies that each line of output is preceded by the file name and line number. The -v option reverses the matching, causing non-matched lines to be printed.

# gzip files

# gunzip files

Compress (or expand) the specified files. Generally, a compressed file has the same name as the original file, followed by .gz.

# head files

Prints the first several lines of each specified file.

# hostname

# hostname name

Displays (or sets) the name of the host.

# info

Launches the GNU Texinfo help system.

# init run_level (eg '3')

Changes the system run level to the specified value

# insmod module

Dynamically loads the specified module

# jobs

Displays all background jobs

# ispell files

Checks the spelling of the contents of the specified files

# kill process_ids

# kill -l

Kills the specified processes, sends the specified processes the specified signal (as a number or a name), or prints a list of available

# killall program

Kills all the processes that are instances of the specified program or sends the specified signal to all processes that are instances of the specified program.

# ispell files

Checks the spelling of the contents of the specified files

# ln old new

# ln -s old new

Creates a hard (or soft) link associating a new name with an existing file or directory.

# locate pattern

Locates files with names containing the specified pattern and uses the database maintained by the updatedb command.

# lpq

Prints the entries of the print queue

# lpr files

Prints the specified files

# lprm job

Cancels printing of the specified print queue entries. Use lpq to determine the contents of the print queue.

# ls

# ls files

# ls -a files

# ls -l files

# ls -lr files

Lists (non-hidden) files in the current directory or the specified files or directories. The -a option lists hidden files as well has non-hidden files. The -l option causes the list to include descriptive information, such as file size and modification date. The -R option recursively lists the subdirectories of the specified directories.

Creates the specified directories. The -p option causes creation of any parent directories needed to create a specified directory.

# mkfs -t type device

Creates a file system of the specified typeon the specified device.

# mkswap device

Creates a Linux swap space on the specified hard disk partition.

# more file

Lets the user peruse a file too large to be displayed as a single screen (page) of output. The more command provides many subcommands that let the user navigate the file. For example, the Space key moves forward one page, the b key moves back one page, and the q key exits the program.

# mount

# mount device directory

# mount -o option -t device directory

Prints the mounted devices or mounts the specified device at the specified mount point. (usually a sub-directory of /mnt).

Changes the current user's password, or that of the specified user (reaquires root privileges). The command prompts for the new password.

# ping host

Sends an echo request via TCP/IP to the specified host. A response confirms that the host is operational.

# pr files

Formats the specified files for printing, by inserting page breaks and so on. The command provides many arguments and functions.

# ps

# ps -Aux

Display the processes associated with the current userid or displays a description of each process.

# pwd

Prints the absolute path corresponding to the current working directory.

# reboot

Reboots the system.

# reset

Clears the terminal screen and resets the terminal status.

# rm files

# rm -i files

# rm -f files

# rm -if files

# rm -rf files

Deletes the specified files or (when the -r option is specified) recursively deletes all subdirectories of the specified files and directories. The -i option causes the command to prompt for confirmation; the -f option suppresses confirmation. Because deleted files cannot generally be recovered, the -f option should be used only with extreme care, particularly when used by the root user.

# rmdir directories

# rmdir -p directories

Deletes the specified empty directories or (when the -p option is specified) the empty directories along the specified path.

# shutdown minutes

# shutdown -r minutes

Shuts down the system after the specified number of minutes elapses (requires root privileges). The -r option causes the system to be rebooted once it has shut down.

# sleep time

Causes the command interpreter to pause for the specified number of seconds

# sort files

Sorts the specified files. The command has many useful arguments.

# split file

Splits a file into several smaller files. The command has many arguments.

# su

# su user

# su -

# su - user

Changes the current userid to root or to the specified userid

The - option establishes a default environment for the new userid.

# swapon device

Enable use of the specified device for swapping

# swapoff device

Enables use of the specified device for swapping

# sync

Completes all pending input/output operations

# tail file

# tail - n file

# tail -f file

Prints the last several lines of the specified files. The -n option specifies the number of lines to be printed. The -f option causes the command to continuously print additional lines as they are written to the file.

# talk user

Launches a program that allows a chat-like dialog with the specified user

# tar cvf tar_file files

# tar zcvf tar_file files

Creates a tar file with the specified name, conCreates the specified directories. The -p option causes creation of any parent directories needed to create a specified directory.taining the specified files and their subdirectories. The z option specified that the tar file will be compressed.

# tar xvf tar_file

# tar zxvf tar_file

Extracts the contents of the specified tar file. The z option specified that the tar file has been compressed.

# telnet host

Opens a login session on a specified host

# top

Prints a display of system processes that is continually updated until the user presses the q key.

# traceroute host

Uses echo requests to determine and print a network path to the host

# umount device

Unmounts the specified filesystem

# uptime

Prints the system uptime

# w

Prints the current system users

# wall

Prints a message to each user except those who've disabled message reception

# traceroute host

Uses echo requests to determine and print a network path to the host.

# wc files

Prints the number of characters, words and lines in the specified files.

Thursday, 3 October 2013

In Centos 6/RHEL and other Linux distros, command line programs come with their
own documentation called manual pages or man pages. These are generally written by the developer of the corresponding program and are divided into
number of sections.

Below is the list of
available man sections. Every section has a unique number and
contains only a specific type of man pages.

1 – Executable programs or
commands

2 – System calls ( functions
provided by the kernel )

3 – Library calls ( functions
provided by the library )

4 – Special files

5 – File formats and conventions
( configuration files )

6 – Games

7 – Miscellaneous

8 – System administration commands

Syntax:

$ man <topicname>

View the Man Page of a command

To read the man page of an Linux command, pass the command name as
the argument to the man. The following will display the man page for
passwd command.

$ man passwdPASSWD(1) User utilities PASSWD(1)NAME passwd - change user password
Some topics may even have man pages in more than one section. In such
a case, man command will display the page which has lower section
number.In this example, the passwd command has manual pages in multiple
sections. But, by default, it displays the man page from the section
1.

The
“PASSWD(1)” shown in the 1st line of the man command output
indicates that it is displaying the man page from section 1. The man
page output displays the command name, syntax of the commands,
description of what the command does, options provided by the
command, etc…

View Man Page from a Specific Section

To read the man page from a particular section, provide the
section number as follows. The passwd command has man page in both
section 1 and section 5. By default, if you don’t specify the
section number, it will display man page from section 1.To display man page from section 5, specify the section number as
shown below.

$ man 5 passwd

Now it will display the manual page for /etc/passwd configuration
file, since the section number 5 is for File Formats and Conversions.

List Available Man Sections for a Command

You can also list all the available sections on a particular topic
using -aw option.

$ man -aw printf/usr/share/man/man1/printf.1.gz

View All Man Pages for a Command – Display All Sections

To view all the man pages for a particular topic, use the “-a”
option. You’ll see the lowest-number man page first. When you exit
that page, and press “Enter” the next man page will appear.

$ man -a printf Change the Default Pager used by Man Command

By default man command will use the $PAGER environment variable to
identify which pager to use for showing output. User can change the
pager in which they prefer to see the man page using ‘-P’ option.The following command will display the man page using more command
pager.

$ man -P more printf

Search Man Page against NAME Section

To search the man page against NAME section, use “-f” option
as shown below.

The above command, searches the manual page names, and displays
the description for the given topic if the manual page names, matches
with the given topic. You can also pass multiple topics in the same
command line.

Search Man Page against NAME and DESCRIPTION Section

To search the man page against NAME & DESCRIPTION section, use
“-k” option. It is equivalent to using “apropos” shell
command.